1. Field of the Invention
The invention relates to a combined braking system, particularly for motor vehicles, having wheel brakes which are assigned to a first vehicle axle and can be activated electromechanically or hydraulically, and having wheel brakes which are assigned to a second vehicle axle and can be activated by means of electromechanical actuators, wherein the wheel brakes which are assigned to the second vehicle axle and can be activated electromechanically can be activated in accordance with a braking request which is applied to the wheel brakes assigned to the first vehicle axle, or data derived therefrom via a vehicle bus (e.g. CAN), and/or in accordance with output signals of a pedal travel sensor which is of redundant design and which determines the activation travel of a brake pedal, and wherein some or all of the wheel brakes which can be activated electromechanically comprise a parking brake device which can be actuated by means of an operator control element, having a, for example, electrohydraulic open-loop and closed-loop control unit which is assigned to the first vehicle axle, having in each case an electronic open-loop and closed-loop control unit which is assigned to the electromechanical actuators of the second vehicle axle, having wheel speed sensors whose signals are fed to the electrohydraulic open-loop and closed-loop control unit and/or also the electronic open-loop and closed-loop control units, and having a communication bus between the electrohydraulic open-loop and closed-loop control unit and the electronic open-loop and closed-loop control units.
2. Description of the Related Art
Such a combined braking system is known from international patent application WO 002007014952 A1. It is to be considered a disadvantage of the previously known braking system that when a communication bus which leads from the electrohydraulic open-loop and closed-loop control unit to an electronic open-loop and closed-loop control unit which is assigned to an electromechanical actuator is defective or faulty, the system goes into a fallback level with restricted functionality or even fails completely.